1. Field of the Invention
This invention relates to dental appliance mounting generally and, in particular, to a method and apparatus for removably mounting a dental appliance, such as an artificial tooth, a full or partial denture, a bridge or other appliance in a mouth.
2. Description of the Prior Art
Replacing lost teeth has been the subject of continuing research over the years. The use of complete or removable partial dentures, with clasps or other attachment means for connection to abutment teeth, is still probably the leading approach being used. However, the stability of such dentures is a problem. There can also be a problem with comfort and food impaction between the gingiva and the underside of the denture base. Further, there can be physical and psychological adjustments for those who have difficulty with bulky removable dentures.
U.S. Pat. No. 3,797,114, issued Mar. 19, 1974 discloses a detachable mount for a dental cap and bridge in an attempt to solve the problems discussed above. This involved preparation of a tooth (or teeth) in the same manner as is commonly employed for attaching a permanent cap. However, instead of directly attaching a cap, a coping is fitted and permanently attached to the prepared tooth. One half of a fastening means is secured to the top of the coping. Then a conventional cap with an undersocket sized to fit over the coping is prepared. The remaining half of the fastener is secured in the undersocket to provide a removably retained cap.
While this was an improvement over the prior art at that time, there is still a problem with thoroughly cleaning and keeping healthy the gingival tissues surrounding the base of the coping. Sometimes a complete seating of the coping is not always obtained. Moreover, once the coping has been permanently installed it is most difficult to remove it without damaging either the coping or the prepared part of the tooth beneath it, in the event that decay or other problems occur as a result of an incomplete seal by the cement underneath the coping or other problems that arise.
Dental implants have also become a viable alternative for replacing lost teeth, and offer solutions to patients who can physically accept such implants. However, present implants and appliances do not always completely meet the needs and requirements of a patient.
Dental implants are presently used to support conventional dental appliances having a saddle that overlies and is at least partially supported by gum tissue. Such dental appliances can be permanently or removably connected to the implants. The removable connections may use tiny screws through the appliance to fasten it to implants. Thus the appliance normally must be removed by a dentist. As a result, the appliance is not removed for cleaning and tissue stimulation for extended periods resulting in damage as discussed above.
Alternatively, a so-called implant abutment can be used which can be screwed into a dental implant, and which carries only a coupling means directly on top of the abutment. Since only the coupling means is available for contact with the abutment, a saddle in contact with the gum must be used for support of the appliance and to provide stability to the appliance.
A direct overdenture is also commercially available in a form similar to the implant abutment discussed in the previous paragraph, However, instead of being screwed into a dental implant, this overdenture is provided with a steel shaft for direct cementation in a bore formed in a tooth root. As in the case of the implant abutment in the preceding paragraph, only a coupling means is carried on the top of the direct overdenture. Therefore, a saddle must be used for the appliance to rest on the gum for support and stability.
Thus, a conventional "fixed bridge" is permanently fixed in placed. The "fixed removable bridge" attached by screws must be removed by a dentist. Present implant abutments and direct overdentures require the use of saddles on the appliance. None of these is the best solution.
Bridges and other appliances may be formed to allow access for tissue stimulation and food removal. However, the appliance must be contoured to provide thin necks around tissue areas with open spaces or embrasures between for hygenic purposes. Such appliances have a poor esthetic appearance and still act as food traps.
Esthetics is also a problem with appliances with saddles over gum tissue, and patients may object to their appearance. This is true whether or not the appliance is removable by the patient.
U.S. Pat. No. 4,431,416, issued Feb. 14, 1984 discloses a dental implant system in which a pillar in the upper part of the implant can provide a platform for a coupling device to removably retain an appliance on the implant. However, the appliance 18 requires a saddle resting on gum tissue to insure that bite force is transmitted via the denture to the gum tissue 42, by-passing the implant in the transmission of such force (as noted in Column 6, lines 1 to 6). As noted above the use of a saddle is objectionable, because of appearance, food impaction, etc.
U.S. Pat. No. 4,431,416 also discloses in FIGS. 12 and 13 the use of a pillar 94 that has a frusto-conical head 96 that corresponds to a prepared tooth 92. This plastic version of an implant abutment provides permanent support for a fixed bridge or other appliance that is cemented to head 96, and thus is not removable by the patient.
In addition to the pillar abutment shown in U.S. Pat. No. 4,431,416 just discussed, a conventional implant abutment that has a coupling means associated with it is commercially available from APM-Sterngold. The Sterngold abutment has a threaded shaft attached to the base of the abutment to be received by a threaded bore in a dental implant. The Sterngold abutment discloses a tapered surface extending away from the affixation area. However, this tapered surface is formed only on part of one half of a coupling means and serves only to guide a cup holding the male portion of the coupling means into a seated position on the tapered surface of the one half. Thus, the Sterngold tapered surface does not and cannot directly support an appliance.
Moreover, the Sterngold implant abutment is used to support removable appliances which have a saddle designed to rest on and be supported by gum tissue. The saddle transmits the bite force to the gum tissue and provides stability to the appliance. However, saddles have problems as discussed herein.